This is one of two applications submitted for the proposed clinical trial. This application proposes support for the Clinical Coordinating Center of the Lupus Nephritis Collaborative Study Group and the collaborating clinics. A separate application proposes support of the Biostatistical-Coordinating Center (John M. Lachin, Sc.D., Principal Investigator). The clinical trial to determine the effects of ACE inhibitor therapy is based upon experimental studies which indicate that this pharmacologic intervention can prevent glomerular injury in the diabetic state. The trial is designed to study patients with Type I diabetes who have proteinuria of more than 500mg/24hrs and a serum creatinine of less than 2.5mg/dl. Because the primary purpose of the study is to determine whether the intrarenal effects of the ACE inhibitor, captopril alters the expected progressive decline in renal function, blood pressure will be carefully controlled in both the experimental and placebo groups. This clinical trial will involve 20-25 collaborating clinics who will admit 400 patients during a 2 yr. recruitment. The mean follow-up will be 3 yrs. The primary end point is halving of the glomerular filtration rate as defined by doubling of the serum creatinine to at least 2mg/dl. The primary goals of the Study are to determine whether ACE inhibitor therapy prevents the progress of Type I diabetic glomerulopathy with respect to significantly decreased: a) rate of loss of GFR b) urine protein excretion rate c) end stage renal failure rate d) mortality rate. The secondary goals of the Study are to 1) follow the "natural history" of a large group of patients with glomerulopathy associated with Type I diabetes mellitus who are managed by controlling their systemic hypertension but have not received ACE inhibitor or calcium channel blocking agents. 2) provide for the controlled evaluation and assessment of progressive retinopathy in a large group of Type I diabetic patients whose systemic hypertension is very closely controlled.